@CuriousKit, your [BZHI thing](https://gitlab.com/freepascal.org/fpc/source/-/merge_requests/315) is very cool at times, except when it triggers on `or` and `xor`. This example compiled for x86-64 with `-CpCOREAVX2 -OpCOREAVX2`: ```pascal procedure Verify(const op: string; got, expected: SizeUint); begin write('%10101010 ' + op + ' %111 = %' + BinStr(got, 1 + BsrQWord(got or 1))); if got = expected then writeln(' - ok') else writeln(' - FAIL, must be %' + BinStr(expected, 1 + BsrQWord(expected or 1))); end; var b, nbits: SizeUint; begin nbits := 3 + random(0); b := %10101010 + random(0); b := b or (SizeUint(1) shl nbits - 1); Verify('or', b, %10101111); b := %10101010 + random(0); b := b xor (SizeUint(1) shl nbits - 1); Verify('xor', b, %10101101); b := %10101010 + random(0); b := b and (SizeUint(1) shl nbits - 1); Verify('and', b, %10); end. ``` outputs: ``` %10101010 or %111 = %10 - FAIL, must be %10101111 %10101010 xor %111 = %10 - FAIL, must be %10101101 %10101010 and %111 = %10 - ok ```